For a photometer or an exposure control unit for the camera, a technique for correct exposure has been put to practical use in which a photographing screen is divided into plural areas to acquire a plurality of brightness information for the field, and it is discriminated whether or not a back light is present on the basis of the plurality of brightness information in accordance with a predetermined algorithm. In Japanese Patent Laid-Open No. 6-225205, such conventional technique was described. According to Japanese Patent Laid-Open No. 6-225205, the photographing screen is divided into a plurality of blocks, and the photometric value data is obtained from cumulative data for each block and the maximum value within the screen. Also, an iris control is made by changing a photometric reference value depending on whether a central part of the screen is a back light state or a follow light state, enabling the correct iris operation to be made for photographing under the back light condition. In Japanese Patent Laid-Open No. 6-225205, a video camera is taken as an example, in which the term of iris operation is used, but has the same meaning as the exposure control for the still camera to make the correct exposure for an image sensing element or film.
A typical example of the condition called back light is a situation where the brightness is low in a central part and a central lower part of the screen and high in other upper part and left and right parts of the screen, as shown in FIG. 3 of Japanese Patent Laid-Open No. 6-225205. In this situation, there is a high possibility of correct exposure by the conventional technique as described in Japanese Patent Laid-Open No. 6-225205. Examining a number of pictures taken under the back light condition, it does not always follow that the back light situation is the above situation where the brightness is low in a central part and a central lower part of the screen and high in other upper part and left and right parts of the screen. Thus, it has been found that there are various patterns, including a pattern where an upper part of the screen is only light and a pattern where a left part of the screen is only light, depending on the composition. For example, FIG. 10A shows one example of photographing composition, in which reference numeral 71 is a portrait area for the principal subject, 72 is a sky area, 73 is a ground area, 74 is a mountain area, and 75 to 77 are the tree areas. When this scene is in the back light, the sky area 72 among these areas has a high brightness, and other areas, particularly the portrait area 71 and the tree areas 75 to 77, have the low brightness. In this scene, an upper-part of the screen is only light, and the left and right parts of the principal subject are dark. Therefore, if this scene is photographed using a photometer as described in Japanese Patent Laid-Open No. 6-225205, it is often difficult to discriminate a back light, irrespective of the back light scene. Thereby, the picture was taken without making exposure compensation and producing the flash in accordance with the back light, and often collapsed black in the portrait area for the principal subject due to underexposure.